Effects of Inadequate Pipe Insulation on a Power Plant's Heat Cycle.

摘要

In the power generation industry, the efficiency of the plant's heat cycle is crucial in the age of de-regulation. As competition increases, the cost of generating electricity must decrease. To lower costs, nuclear power plants are always looking at ways of recovering lost megawatts. Additionally, plants are striving to maintain high availability, especially during the peak load demands. At the Limerick Generating Station (LGS), the System Manager was tackling both challenges. He determined that Unit #1 Drywell temperatures had been historically higher than Unit #2 Drywell temperatures. The Drywell is a concrete primary containment that houses both the nuclear reactor and recirculation pumps in a Boiling Water Reactor (BWR) plant. A driving force to resolve the higher temperatures was the plant's Technical Specifications which dictate a maximum allowable temperature of 135 deg F in the Drywell. During the summer of 1999 (one of the hottest on record for the East coast), the temperatures in the Unit #1 Drywell approached the maximum allowed by the Technical Specifications. Exceeding this temperature would require Unit #1 to reduce power during a critical demand period or even shut down. During a peak load condition, the loss of generating capabilities could be extremely costly for the utility. In extreme circumstances, as recent as the winter of 2001 in California, customers could be faced with the potential of roaming brown outs due to the reduced capacity on the electrical grid. Based on the System Manager's experience, the heat source was suspected to be from less than adequate insulated pipes in the Drywell. To determine the condition and status of the insulation, infrared was used to inspect the pipes. The ideal condition is to observe the maximum temperatures when the reactor is at 100 percent power, but due to the radiological and atmospheric conditions in the Drywell, the inspection would have to be performed immediately after the reactor was shut down for an outage. The initial inspection of the Drywell piping was limited to 30 minutes due the ambient temperature exceeding 130 deg F. The infrared inspection quickly identified numerous thermal anomalies that included aging and worn insulation, not insulated and inadequately insulated pipes, valves and pipe hangers. Insulation repairs were performed during the outage. Although a visual inspection is adequate in finding pipes not insulated, infrared was needed to identify the specific sections of insulation requiring repair. The post outage results indicated that the Drywell temperature dropped an average of 3 deg F, thus insuring adequate margin for the Drywell temperature Technical Specification requirements.